This art­icle expands on the first in the series “Inter­lock Archi­tec­tures – Pt. 1: What do those cat­egor­ies really mean?”. Learn about the basic cir­cuit archi­tec­tures that under­lie all safety inter­lock sys­tems under ISO 13849 – 1, and CSAZ432 and ANSIRIAR15.06.